The use of robotics to perform welding operations is well known. Typically, robots are used to increase production and/or to reduce human exposure to harsh and/or undesirable working conditions. Such systems may include an arc welding robot which moves a welder toward an object which is fixed to a welding jig. The system welds the object while moving the object and/or the welder. A control program controlling the movement of the robot, operates on the basis of certain stored input parameters, such as the type of welding object, geometric data of the welding portion, the depth of penetration, and the starting and termination points of the welding. Certain welding conditions which may be considered in the creation of the control program include welding current, welding voltage, distance between the welder and the welding object, speed of supplying a wire, as well as a relative velocity of the welder and the welding object. In an open-loop control system these welding parameters are applied without any alteration during the welding operation.
The inability to alter the welding process in an open-loop system has in certain situations been considered a drawback. Therefore robotic systems have been designed to include feedback control in order to alter the welding process during the welding operation. For example, U.S. Pat. No. 6,118,093, hereby incorporated by reference in its entirety, proposes a closed-loop design where real-time changes of welding conditions such as a welding voltage, welding current, welding speed and the like are performed without interruption of welding operation. These changes are achieved by the use of a temperature detection process, used to generate feedback data to a controller. Adjustments are made to the welding process dependent on the feedback data.
Other closed-loop robotic welding systems incorporate vision capabilities. In one example, a laser directs its beam across the seam of a welding area to generate a feed back signal for the robotic controller. Based on this feedback signal, adjustments to the welding operation are undertaken. For example, movement of the welding torch is adjusted based on the provided information.
The exemplary described robotic systems have various drawbacks. Specifically, with regard to existing open-loop robotic systems, the control programs are customized to operate for a specifically sized and shaped workpiece. To obtain an economic benefit when using these types of welding systems, a large number of the identically configured and sized workpieces must be batch processed. When another sized workpiece is to be welded, a separate unique customized control program must be created. Attempting to weld a workpiece using a control program created for a different sized workpiece will result in defective welding due to misplacement of the welder. Thus, existing open-loop welding systems do not provide, economical process to weld a number of differently sized cylindrical workpieces, where such a system is able to economically weld part-volumes as small as a single part.
On the other hand, while robotic systems having a closed-loop design permit for alterations to the welding process dependent upon existing conditions, the inclusion of these feedback systems greatly complicate and increase the cost of the welding systems. For example, a laser vision system incorporated with the robotic arm, may cost as much as the robotic system itself. Thus, the cost of adding feedback controls to alter a welding procedure creates economic inefficiencies when attempting to weld small numbers of workpieces. The economic benefit of automating the welding process is therefore offset by the high cost of incorporating the components needed for a closed-loop system.
A further drawback of existing robotic systems, is their failure to address the ability to weld two cylindrical workpieces not completely in the same horizontal plane. More specifically, in robotic welding, it has been defined that the cylindrical workpiece is rotated 360° while being welded. However, existing systems apparently only address the welding of two cylindrical workpiece portions which are in the same horizontal plane.
Another drawback in existing robotic systems, is the inability to provide for operator interaction during the welding process, which permits for refined operator control of the location of the welder, even while the welding control program is functioning.
In view of the foregoing problems and shortcomings of existing cylindrical robotic welding systems, the present application describes a method and apparatus to overcome these shortcomings, and provide an improved cylindrical robotic welding system.